Electromagnetic radiation traveling through any transmission medium suffers from attenuation. In fact, the farther electromagnetic radiation travels through a transmission medium the more the radiation losses strength. Computational and communication systems that process and transmit information encoded in electromagnetic radiation may avoid this problem by amplifying or increasing the strength of the electromagnetic radiation at points along the transmission path. An electromagnetic radiation amplifier is a device that can be placed at points along the transmission path to increases the amplitude of incident electromagnetic radiation. FIG. 1 illustrates operation of an electromagnetic radiation amplifier 100. Ideally, the amplifier 100 receives an incident coherent beam of electromagnetic radiation represented by a first plane wave 102 and emits a higher intensity coherent beam of electromagnetic radiation, which is represented by a second plane wave 104 with a larger amplitude than the incident coherent beam of electromagnetic radiation 102. The amplified coherent beam of electromagnetic radiation propagates in substantially the same direction and with substantially the same wavelength λ and phase as the incident coherent beam of electromagnetic radiation 102.
As part of the amplification process, an electromagnetic radiation amplifier includes a gain medium that is pumped or energized into a higher energy electronic state. Pumping a gain medium is typically accomplished using either electromagnetic radiation emitted from an external laser source or an electrical signal. After the gain medium is pumped, the incident coherent electromagnetic radiation stimulates emission of electromagnetic radiation within the gain medium. This stimulated electromagnetic radiation has substantially the same direction, wavelength, and a fixed phase relationship with the incident electromagnetic radiation and constructively interferes with the incident electromagnetic radiation producing an amplified coherent beam of electromagnetic radiation.
Doped fiber amplifiers are a commonly used amplifier. The gain medium of a typical doped fiber amplifier is comprised of a fiber optic core that has been doped with atoms and is surrounded by a cladding layer. Pump electromagnetic radiation from an external laser excites the atoms into higher energy electronic states. An incident beam of electromagnetic radiation to be amplified is transmitted through the core and stimulates emission of electromagnetic radiation with substantially the same phase, wavelength, and direction from the excited atoms, which, in turn, yields via constructive interference an amplified coherent beam of electromagnetic radiation. The core guides the pump electromagnetic radiation and the amplified coherent beam of electromagnetic radiation. Semiconductor amplifiers are another type of commonly used electromagnetic radiation amplifier. The gain medium of a semiconductor amplifier typically comprises a pn-junction layer located between a positively doped semiconductor region and a negatively doped semiconductor region. An incident coherent beam of electromagnetic radiation to be amplified is directed into the pn-junction layer and is amplified when the incident electromagnetic radiation stimulates emission of electromagnetic radiation produced by recombining electron-holes pairs within the pn-junction layer. This electromagnetic radiation also has substantially the same phase, wavelength, and direction as the incident electromagnetic radiation and also yields via constructive interference an amplified coherent beam of electromagnetic radiation
Doped optical fiber amplifiers and semiconductor amplifiers can be fabricated to amplify signals over a broad range of frequencies, however these amplifiers typically cannot be designed to amplify electromagnetic radiation selectively in a narrow range of frequencies without creating a disturbance at the other frequencies. In addition, a doped fiber amplifier is typically too large to be coupled with micro scale and nanoscale optical devices. Although semiconductor amplifiers can be fabricated on the micro scale, the structural difference between semiconductor amplifiers and optical fibers makes it difficult to couple an optical fiber with the pn-junction layer of a semiconductor amplifier. Physicists and engineers have recognized a need for electromagnetic radiation amplifiers that can amplify a coherent beam of electromagnetic radiation over selected narrow frequency ranges and are small enough to be implemented in a variety of micro scale and nanoscale optical devices.